Astronomers today released the largest-ever compilation of exoplanet-detecting observations made with a technique called radial velocity. They also demonstrated how these observations can be used to hunt for exoplanets by detecting 114 potential exoplanets, including one orbiting a star 8.1 light-years away.
Artist’s concept of the super-Earth exoplanet GJ 411b. Image credit: Ricardo Ramirez.
The radial velocity method is one of the most successful techniques for finding and confirming exoplanets.
It takes advantage of the fact that in addition to an exoplanet being influenced by the gravity of the star it orbits, the exoplanet’s gravity also affects the star.
Astronomers are able to use sophisticated tools to detect the tiny wobble the exoplanet induces as its gravity tugs on the parent star.
The newly available observations were taken by the High Resolution Echelle Spectrometer (HIRES), an instrument mounted on the Keck Observatory’s 10-m telescope at Mauna Kea in Hawaii.
HIRES is designed to split a star’s incoming light into a rainbow of color components. Astronomers can then measure the precise intensity of thousands of color channels, or wavelengths, to determine characteristics of the starlight.
For two decades, they have pointed HIRES at 1,624 nearby stars, all within a relatively close 325 light-years from Earth.
The instrument has recorded 60,949 observations, each lasting anywhere from 30 sec to 20 min, depending on how precise the measurements needed to be.
With all these data compiled, any given star in the dataset can have several days’, years’, or even more than a decade’s worth of observations.
“This dataset will slowly grow, and you’ll be able to go on and search for whatever star you’re interested in and download all the data we’ve ever taken on it,” said Dr. Jennifer Burt, an astronomer at MIT’s Kavli Institute for Astrophysics and Space Research and co-author of a paper accepted for publication in the Astronomical Journal.
“The dataset includes the date, the velocity we measured, the error on that velocity, and measurements of the star’s activity during that observation.”
The huge dataset is now available to the public, along with an open-source software package to process the data and an online tutorial.
By making the data public and user-friendly, the astronomers hope to draw fresh eyes to the observations.
“This is an amazing catalog, and we realized there just aren’t enough of us on the team to be doing as much science as could come out of this dataset,” Dr. Burt said.
“We’re trying to shift toward a more community-oriented idea of how we should do science, so that others can access the data and see something interesting.”
Within the newly available dataset, Dr. Burt and colleagues highlighted more than 100 stars that are likely to host exoplanets but require closer inspection, either with additional measurements or further analysis of the existing data.
“We tabulate a list of 357 significant periodic signals that are of constant period and phase, and not coincident in period and/or phase with stellar activity indices,” they said.
“These signals are thus strongly suggestive of barycentric reflex motion of the star induced by one or more candidate exoplanets in Keplerian motion about the host star.”
“Of these signals, 225 have already been published as planet claims, 60 are classified as significant unpublished planet candidates that await photometric follow-up to rule out activity-related causes, and 54 are also unpublished, but are classified as ‘significant’ signals that require confirmation by additional data before rising to classification as planet candidates.”
The astronomers also confirmed the presence of a super-Earth exoplanet around a star called GJ 411, also known as Lalande 21185 and HD 95735.
At a distance of 8.1 light-years, it is the fourth-closest main sequence star to our own Solar System and is only about 40% the mass of the Sun.
The planet, named GJ 411b, has a mass 3.8 times that of Earth’s and a very short orbital period of 9.9 days.
“There seems to be no shortage of exoplanets. There are a ton of them out there, and there is ton of science to be done,” Dr. Burt said.
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R. Paul Butler et al. 2017. The LCES HIRES/Keck Precision Radial Velocity Exoplanet Survey. Astronomical Journal, in press;
